Facile synthesis of cassava starch-based bioplastics modified by citric acid-epoxidized soybean oil oligomers

The present work aimed to explore the effect of citric acid (CA) on the structures and properties of cassava starch/epoxidized soybean oils-based bioplastics. First, citric acid-epoxidized soybean oil oligomers (CESO) were fabricated by the reaction of epoxidized soybean oils (ESO) and CA with different molar ratios (n(CA):n(epoxy) = 3 similar to 12). CESO were successfully synthesized as evidenced by the FTIR and GPC data. Second, the synthesized CESO were applied to fabricate the bioplastics with starch by solution casting. The prepared bioplastics were evaluated by structural, thermal, mechanical, optical, and water resistance properties. The FTIR spectra reflected that CESO showed an esterification reaction with starch. The FESEM images revealed that CESO exhibited better dispersity in the samples than ESO. The samples containing CESO got plasticized with a remarkable increase of elongation at break (3.41-6.14 times) and a decrease of the tensile strength (1.35-2.07 times) compared to that with ESO. CESO promoted significantly higher light transmittance of the bioplastics than ESO due to their better dispersibility in the bioplastics. The hydrophobicity of the bioplastics increased upon the addition of CESO. These results made the fabricated bioplastics potential substitutes for petroleum-based plastics for industrial applications.